feat: add --no-variable-replacement flag to disable pattern variable substitution

- Introduce CLI flag to skip pattern variable replacement.
- Wire flag into domain request and session builder.
- Avoid applying input variables when replacement is disabled.
- Provide PatternsEntity.GetWithoutVariables for input-only pattern processing support.
- Refactor patterns code into reusable load and apply helpers.
- Update bash, zsh, fish completions with new flag.
- Document flag in README and CLI help output.
- Add unit tests covering GetWithoutVariables path and behavior.
- Ensure {{input}} placeholder appends when missing in patterns.

README.md

@@ -591,6 +591,7 @@ Application Options:
       --printsession=               Print session
       --readability                 Convert HTML input into a clean, readable view
       --input-has-vars              Apply variables to user input
+      --no-variable-replacement     Disable pattern variable replacement
       --dry-run                     Show what would be sent to the model without actually sending it
       --serve                       Serve the Fabric Rest API
       --serveOllama                 Serve the Fabric Rest API with ollama endpoints